Crystal structures and Hirshfeld surface analyses of N,N-dimethylacetamide–1-(dimethyl-λ4-azanylidene)ethan-1-ol tribromide (1/1), N,N-dimethylacetamide–1-(dimethyl-λ4-azanylidene)ethan-1-ol dibromidoiodate (1/1) and N,N-dimethylacetamide–1-(dimethyl-λ4-azanylidene)ethan-1-ol dichloridoiodate (1/1)

In all three title crystals, the cations are linked by O—H⋯O and/or C—H⋯O hydrogen bonds. The three-dimensional packing is further consolidated by strong halogen–hydrogen and weak van der Waals interactions.


Chemical context
Halogenation is a chemical reaction that involves the introduction of one or more halogen atoms to an organic compound. Usually, either direct replacement of hydrogen by a halogen atom or addition of a halogen molecule to double and triple bonds are used. The pathway and stereochemistry of halogenation reactions are strongly dependent on the halogenating agent. However, halogens and interhalogens are very harmful to health. An effective source of active halogen should be a safe solid substance well soluble in different solvents, with a low pressure of halogen vapour and high content of the active halogen. As a source of halogens, molecular complexes with N-and O-nucleophiles are widely used. However, the N-halogen succinimides slowly decompose when stored and are poorly soluble in some solvents, while the molecular complexes of halogens with N-and O-nucleophiles (for instance, dioxane dibromide or complexes with pyridine) are short-lived (Abdell-Wahab et al., 1957;Horner et al., 1959;Zaugg et al., 1954;Buckles et al., 1957;Ramachandrappa et al., 1998;Groebel et al., 1960;Mohamed Farook et al., 2006;Sui et al., 2006). In this context, we synthesized inexpensive and readily available bis(N,N-dimethylacetamide) hydrogen trihalides as halogenation agents and source of positively charged halogen ions (Rodygin et al., 1992;Prokop'eva et al., 2008). The amide complexes with halogens are excellent reagents for the functionalization of phenols and anilines (Rodygin et al., 1992;Mikhailov et al., 1993;Safavora et al., 2019). They are also used in the synthesis of mono-halogensubstituted ketones (Rodygin et al., 1994a;Burakov et al., 2001;Abdelhamid et al., 2011;Khalilov et al., 2021) and the halogenation of various alkenes, alkynes (Rodygin et al., 1994b) and bridged epoxy-isoindolones (Zaytsev et al., 2017;Zubkov et al., 2018;Mertsalov et al., 2021a,b). The most famous amide complex, i.e. Povidone-iodine (PVP-I), also known as iodopovidone, is an antiseptic used for skin disinfection before and after surgery (Stuart et al., 2009). Moreover, noncovalent interactions play critical roles in synthesis and catalysis, as well as in forming supramolecular structures due to their significant contribution to the self-assembly process (Gurbanov et al., 2020a(Gurbanov et al., ,b, 2022aMa et al., 2017Ma et al., , 2021Mahmoudi et al., 2017a,b;Mahmudov et al., 2011Mahmudov et al., , 2022. Similar to hydrogen bonding, the halogen bond has also been used in the design of materials (Shikhaliyev et al., 2019). We, thus, analyzed such expected respective intermolecular interactions in the isolated and structurally characterized three title aggregates in the context of the present study.

Figure 4
A view along the a axis of the O-HÁ Á ÁO and C-HÁ Á ÁO interactions in the crystal structure of (I).

Figure 5
A view along the c axis of the O-HÁ Á ÁO and C-HÁ Á ÁO interactions in the crystal structure of (I).
The Hirshfeld surface analysis and the associated twodimensional fingerprint plots over the cations of (I), (II) and (III) were carried out and created with CrystalExplorer17.5 (Spackman et al., 2021). A summary of the short interatomic contacts in (I), (II) and (III) is given in Table 4. The twodimensional fingerprint plots for compounds (I), (II) and (III) are shown in Fig. 10. The principal interatomic interactions for the title compound [Figs. 10(b)-(d) and A view along the b axis of the O-HÁ Á ÁO and C-HÁ Á ÁO interactions in the crystal structure of (II).

Figure 8
A view along the a axis of the O-HÁ Á ÁO interactions in the crystal structure of (III).

Figure 9
A view along the c axis of the O-HÁ Á ÁO interactions in the crystal structure of (III).

Figure 6
A view along the a axis of the O-HÁ Á ÁO and C-HÁ Á ÁO interactions in the crystal structure of (II).

Database survey
A database search was carried out using ConQUEST ( (Gubin et al., 1988) and SEGMOG01 ].
In the crystal of HDMAAU (space group: monoclinic P2 1 a, Z = 2), the structure consists of distinct [AuCl 4 ] À anions and [H(dma) 2 ] + cations, with the gold and the bridging H atoms located at centres of symmetry. The hydrogen bond is 'symmetrical' as a result of crystallographic requirements. The OÁ Á ÁO distance is 2.430 (16) Å . Thermal motion analysis indicates that methyl groups attached to nitrogen have higher rotational amplitudes, resulting in short apparent C-H bond lengths [average 0.96 (4) Å ] compared with the methyl group attached to a carbonyl C atom which has an average C-H bond length of 1.02 (2) Å .
In the crystal of SEGMOG (space group: monoclinic P2 1 c, Z = 2), two N,N-dimethylacetamide molecules in the asymmetric unit are connected to each other by an O-HÁ Á ÁO hydrogen bond, essentially sharing the central H atom. These molecules and the Br-Br-Br groups are arranged in columns parallel to the a axis. The arrangement is consolidated in the crystal packing by van der Waals interactions between these columns.
In the crystal of SEGMOG01 (space group: monoclinic P2 1 n, Z = 2), the unit-cell parameters and the arrangement of the molecules are relatively similar to the older structure (SEGMOG), while the H atom bridging the the two acetamides was not refined.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. In compounds (I), (II) and (III), the C-bound H atoms were positioned geometrically, with C-H = 0.98 Å (for methyl H atoms), and constrained to ride on their parent atoms, with U iso (H) = 1.5U eq (C). The hydroxy H atoms were found in the difference Fourier maps and their coordinates were refined freely, with U iso (H) = 1.5U eq (O). In (I), the H atom of the OH group is located in a special position (1.0, 0.5, 1.0) with an occupancy of 0.5 for the rrefined atom. In (II), the H atoms of the OH groups are disordered over two positions, with occupancies of 0.49 and 0.51. In (III), the H atom of the OH group was refined with an occupancy of 0.25 for its position close to an inversion centre in between the O atoms of two acetamides and simultaneously residing on a mirror plane.  N,N-dimethylacetamide-1-(dimethyl-λ 4 -azanylidene)ethan-1-ol tribromide (1/1), N,N-dimethylacetamide-1-(dimethyl-λ 4 -azanylidene)ethan-1-ol dibromidoiodate (1/1) and   N,N-dimethylacetamide-1-(dimethyl-λ 4 -azanylidene)

N,N-Dimethylacetamide-1-(dimethyl-λ 4 -azanylidene)ethan-1-ol dibromidoiodate (1/1) (II)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (

Refinement
Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = 0.008 wR(F 2 ) = 0.022 S = 1.06 1745 reflections 52 parameters 0 restraints Primary atom site location: dual Hydrogen site location: mixed H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0153P) 2 + 0.0381P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.46 e Å −3 Δρ min = −0.25 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.